Conventionally, a typical vehicle brake system has a pump that is driven to generate a required braking force based on the brake pedal operation. In such a brake system, for example, brake fluid discharged from the pump is introduced into a master cylinder (hereinafter referred to as M/C) to push an M/C piston, which in turn generates brake fluid pressures in wheel cylinders (hereinafter referred to as W/Cs). In a hydraulic servo type brake system, brake fluid discharged from the pump is introduced into a hydro booster through a regulation valve to increase pressure thereof. The pressurized brake fluid is introduced into the W/Cs through the M/C and used for generating W/C pressures.
The above brake system requires many parts. That is, a regulation valve, a pump and conduits for carrying the brake fluid are required. Because a pump is required for increasing the brake fluid pressure, brake system energy efficiency is often decreased, and the pump typically generates undesirable noise.